1. Field of the Invention
This invention relates to a sheet metal poly-V pulley having poly-V grooves formed at specified pitches in the peripheral wall of a cup-shaped blank, and a manufacturing method thereof.
2. Prior Art
Conventionally, sheet metal poly-V pulleys of this type, that is, poly-V pulleys made of sheet metal and having a plurality of V-grooves, or so-called poly-V grooves, formed at specified pitches on the peripheral wall of a cup-shaped blank possessing a bottom wall and a peripheral wall formed by deep drawing of sheet metal blank, have been sold and used widely as intermediate conduction poly-V pulleys in, for example, vehicle engines.
Incidentally, this kind of sheet metal poly-V pulley, unlike the cast product, is very lightweight because thin sheet metal blank is drawn, rolled and processed. The transmission of rotation to the belt, which is wound around the pulley is very high, so that the belt is efficiently driven at high speed. Aside from such advantages, the strength of the poly-V belt, to be wound around the sheet metal poly-V pulley, is extremely improved and, due to such enhancement, the poly-V belt is not subject to breakage if the sheet metal poly-V pulley is rotated at a considerably high speed. That is, in order to rotate the poly-V belt at high speed, the belt must be wound around and engaged with the sheet metal poly-V pulley at a very high tension, and if rotated by winding and engaging at such high tension, the poly-V belt is not subject to breakage.
However, as stated above, when rotated under high tension and in engagement by winding, since the poly-V pulley is made of a think sheet metal blank, plastic deformation of the pulley is likely to occur in the peripheral wall and bottom wall, or at points crossing parts of the bottom wall and peripheral wall. Hence, it is sometimes difficult to cope with the increasing strength of poly-V belts.
In this case, to prevent deformation of the sheet metal poly-V pulley, it may be possible to use a considerably thicker sheet metal blank, but this results in an increase in the cost of materials and difficulties in the manufacture of the sheet metal poly-V pulley from a thicker sheet metal blank. Also, increases in the weight of the pulley may sacrifice the advantages of the sheet metal poly-V pulley.